1. Field of the Invention
The present invention generally relates to a communication system. More particularly, the present invention relates to an apparatus and method of scheduling data packet in a communication system.
2. Description of the Related Art
FIG. 1 is a schematic view illustrating the configuration of a typical communication system.
Referring to FIG. 1, the communication system has a multi-cell structure. That is, the communication system includes cells 100 and 150, a Base Station (BS) 110 covering the cell 100, BS 140 covering the cell 150, and a plurality of Mobile Stations (MSs) 111, 113, 130, 151 and 153.
The communication system is being developed to additionally provide high-speed large-data packet transmission service to MSs, especially services with a variety of Quality of Service (QoS) requirements. Parameters that determine the QoS of data packets are allowed transmission delay time, fading characteristics, a closeness between a transmitter and a receiver, and a use or a non-use of diversity. Therefore, for reliable data packet transmission and reception, data packets should be scheduled in a manner taking into account a QoS of the data packets.
FIG. 2 is a flowchart illustrating an operation in a scheduler for scheduling data packets so as to satisfy the QoS requirements of the data packets, which are determined according to allowed transmission delay time of the data packets in a typical communication system.
As QoS levels are determined according to allowed transmission delay time, data packets are categorized into real-time data packets and non-real time data packets. If the data packets can be packed the scheduler schedules the data packets according to the number of data packet connections. If the data does not allow for packing, the scheduler schedules the data packets according to the number of the data packets. For convenience' sake, it is assumed that the scheduler schedules data packets according to the number of the data packets, and the scheduling is carried out on a frame basis in the illustrated case of FIG. 2.
Referring to FIG. 2, thus, the scheduler monitors the presence or absence of real-time data packets at a scheduling time in step 211. In the absence of real-time data packets, the scheduler prioritizes non-real time data packets for transmission and schedules the non-real time data packets according to their priority levels in step 213. Then the scheduler ends the algorithm.
In the presence of real-time data packets in step 211, the scheduler prioritizes real-time data packets for transmission and schedules the real-time data packets according to their priority levels in step 215. Then, in step 217, the scheduler prioritizes the non-real time data packets for transmission and schedules the non-real time data packets according to their priority levels. The scheduler ends the algorithm.
As described above, when the scheduler schedules data packets so as to satisfy the QoS levels of the data packets which have been determined taking into account the allowed transmission time of the data packets, scheduling of non-real time data packets follows scheduling of real-time data packets in the typical communication system. Because it is important to keep the probability of failing to transmit real-time data packets within an allowed transmission time at or below a predetermined value, the real-time data packets takes priority over non-real time data packets in transmission.
However, the wireless channel environment under which the communication system is usually placed varies with data packet transmission speeds of MSs. To improve a total performance of the communication system, it is preferable to transmit data packets when the wireless channel environment becomes good. If scheduling is performed such that non-real time data packets are always behind real-time data packets in priority, even though a sufficient allowed transmission delay time is left for the real-time data packets in a relatively poor wireless channel environment, the real-time data packets take priority over the non-real time data packets. In the opposite case, even when the wireless channel environment is relatively good, if no resources are available for the non-real time data packets after scheduling the real-time data packets, transmission of the non-real time data packets is impossible.
Accordingly, there exists a need for a new scheduling method that considers a wireless channel environment in addition to allowed transmission delay time.